Fig. 6From: Chemical and structural characterization of α-N-acetylgalactosaminidase I and II from starfish, asterina amurensis Double displacement catalytic mechanisms of starfish α-GalNAcase I and II. Step 1: D140 from α-GalNAcase makes a nucleophilic attack on C1 of terminal α-GalNAc of substrate, cleaving the glycosidic linkage and producing a covalent intermediate complex. Step 2: A water molecule, deprotonated by D201, makes a nucleophilic attack on C1 of α-GalNAc and cleave the covalent enzyme-substrate intermediate complex and release N-acetylgalactosamineBack to article page